The HD Zuchtwert or Breed
Value Number

HD ZUCHTWERT (ZW)

BREED VALUE ASSESSMENT
NUMBER

The HD ZW value factors in many variables in
the calculation, but is based mostly on the hips status of a dog's progeny. This
is critical in the usefulness of the HD ZW. The dog's own hip status is only one
of several important variables in the equation, not the sole determinate. This
is because it is possible for a dog with excellent hip status to produce a
number of progeny with HD and conversely, a dog with fair hip status can produce
a majority of progeny with excellent hip status. Without factoring in this
critical look at the dog's Genotype (what his genes pass on to progeny) in
addition to his Phenotype (what his actual hip status is), real progress cannot
be made in reducing the incidence of HD.

So how does it work? Each dog registered with
the SV is assigned an HD ZW number at birth, based on its parents HD ZW numbers.
Also all dogs born in the United States whose hip x-rays are sent to the German
SV for their a-stamp certification are also assigned an HD ZW score, which is
based upon their own certification results and that of their parents if they are
also in the HD ZW registry. After a dog is x-rayed, its own hip status is
factored into his HD ZW. Upon producing progeny of his own, the results of the
progeny's x-rays are then factored into the parents HD ZW numbers. The HD ZW
number is not a static value. It fluctuates depending on what the dog produces!
This is what is important: A dog's Genotype, what the dog produces. Not his
Phenotype, what his actual hip status is.

An HD ZW value of 100 has been set as the
breed average. HD ZW values less than 100 mean the dog produces fewer progeny
with HD than the breed average. A number greater than 100 means a dog produces
HD more often that the breed average or comes from parents with high hip scores
for the same reason. Rarely does a dog have a score of less than 70, but there
are some that do have scores into the 60s. So HD ZW values less than 100 are the
most desirable. However, the focus must still be on the total dog. Breeding
decisions need to include much more than only a dog's HD ZW, Working ability and
temperament are also very important.

To allow this, the SV requires that the
calculated HD ZW for progeny of a desired mating be 100 or less. So a female
with an HD ZW of 80 can be bred to a male with an HD ZW number as high as 120.
The pups of a breeding like this would be assigned HD ZW values of 100 at birth.
So HD ZW values less than 100 are not only desirable, but they offer greater
options in breeding partners. Additionally, stud dog owners can prove their
dog's prepotency by accepting breedings to females with higher HD ZW values.